Numerous magnetic regulating devices of this type have been proposed in the prior art. U.S. Pat. No. 2,762,222, which discloses such a regulating device, may be cited by way of example.
FIGS. 1 and 2 show schematic views of a typical prior art regulating device wherein a resonant structure 1, having a general “C” shape, carries a fixed permanent magnet 2 so that the two free ends of the “C” form two magnetic poles 8 and 10, thereby delimiting an air gap E. Magnet 2 is fixed to the base of the “C” via an elastic structure 4, which is fixed in turn to a frame B by screws 6. An escape wheel 12, made of a material of high magnetic permeability, is arranged such that its teeth 12a pass into air gap E. Each tooth 12a of wheel 12 is hollowed to form a ferromagnetic path 14 of sinusoidal shape. Wheel 12 is driven in rotation by a driving torque, symbolised by the arrow C, derived from a barrel which is not shown. When escape wheel 12 turns, the magnetic poles 8, 10 of the resonator 1, tend to follow the sinusoidal ferromagnetic path 14 defined by escape wheel 12. In doing so, resonator 1 starts to vibrate in the radial direction R of escape wheel 12 until it reaches its natural frequency in steady state. With an ideal resonator, this natural frequency is substantially independent of the driving torque. The resonator is maintained by the transmission of energy from the escape wheel 12 driven by the barrel. The velocity of escape wheel 12 is thus synchronised with the natural frequency of oscillator 1.
To date, magnetic escapements of this type have not been integrated in wristwatches due their high shock sensitivity. Indeed, in the event of shocks, the oscillating structure or the oscillating magnet may move away from the ferromagnetic path and break the magnetic coupling between the oscillating structure and said path. In that case, the escape wheel is driven by the driving torque in an uncontrolled manner. Two situations may arise depending on the nature of the shock. Either, when there is a shock, the escape wheel jumps one or more step and then synchronises again with the oscillating structure, which leads to a loss of state impairing the chronometric performance of the watch. Or, the intensity and/or duration of the shock are such that the magnetic coupling between the wheel and the oscillating structure is permanently lost, this phenomenon is generally denoted by the term “uncoupling”. The oscillating structure then stops oscillating and the escape wheel is driven in rotation in an uncontrolled manner until the mainspring barrel is totally let down.
To overcome this problem, a first solution has been proposed consisting in strengthening the magnetic coupling between the escape wheel and the oscillating structure, for example, by reducing to a minimum the distance between the magnetic poles and the wheel. However, this solution is not entirely satisfactory in that it limits the possibilities of the wheel self-starting or presents problems of locking caused by the poles sticking on the escape wheel.
A second attempt to overcome this problem consisted in providing a plurality of mechanical stop members arranged on either side of the ferromagnetic path against which the oscillating magnet abuts as soon it moves away from its coupling path. Although this device can prevent the uncoupling of the escape wheel, it increases the size of the system and induces perturbations in the oscillating structure with every shock against the stop members, resulting in decreased chronometric performance in a similar manner to the problem of knocking in a conventional Swiss lever escapement.
It is therefore a main object of the invention to overcome the drawbacks of the aforecited prior art by providing a magnetic device for regulating the relative angular velocity of a wheel and of an oscillating structure of the type described above, including means intended to reduce or eliminate shock sensitivity (hereafter denoted as “anti-uncoupling means”).
It is also an object of the invention to supply a regulating device of this type wherein the anti-uncoupling means do not use energy derived from the barrel in normal operation.
It is also an object of the invention to provide a regulating device of this type wherein the anti-uncoupling means do not adversely affect the self-starting of the system.
It is also an object of the invention to provide a regulating device of this type wherein the anti-uncoupling means do not cause any friction and consequently any wear, dust or noise.
It is also an object of the invention to provide a regulating device of this type wherein the anti-uncoupling means do not increase the size of the device.
It is also an object of the invention to provide a regulating device of this type wherein the anti-uncoupling means are reliable, economical and easy to implement.